1. Field of the Invention
The present invention is directed to a device for generating signals dependent on the respiratory activity of a patient, and in particular to such a device adapted for generating trigger signals for a medical diagnosis and/or therapy apparatus.
2. Description of the Prior Art
Body organs and anatomical structures are considerably displaced dependent on the respiratory activity of a patient. It is therefore necessary, for satisfactory results, in many medical examination and therapy methods, to synchronize the operation of the examination or therapy equipment with the respiration cycle of the patient. For example, individual measurements can be triggered when a defined respiratory condition is reached. For example, in computer tomography devices, such synchronization is needed for the creation of dynamic computer tomograms, wherein a chronological succession of identical anatomical structures is to be acquired at each measurement event. Data sets for three-dimensional or multi-planar reconstructions in computer tomography should also frequently be synchronized with the patient's respiration. In these types of measurements, tomograms of an organ or organs are taken at precisely defined spacings in chronologically successive measurements. The respiratory condition of the patient must be reproduced for each individual measurement, so that organ dislocations due to the respiration activity do not appear in the successive measurements. Similar requirements are present, for example, in magnetic resonance imaging and in lithotripsy, wherein a shock wave for disintegrating a calculus is triggered dependent on the patient's respiratory condition.
In addition to being capable of identifying any point (i.e., respiratory condition) within a patient's respiratory cycle, it is also desireable to define a respiratory condition in terms of absolute values. This is of significance, for example, in pulmonary density measurements. It is known to generate electrical signals corresponding to the respiratory condition of a patient by the use of a breathing belt which is tightened around the chest or stomach of a patient, and which generates electrical signals based on the expansion and contraction of the belt which occurs as the patient breathes. This is not a satisfactory solution, because no absolute measurement of the respiratory volumes is possible using this known device, and errors in whatever medical measurement or treatment is being undertaken dependent on the patient's respiratory activity may arise dependent on characteristics which vary from patient to patient, such as the degree to which the patient uses chest or diaphragm respiration.